272 



COMPARATIVE ANATOMY. 



§ 211. 



The gut in the Thysanura, and in most Pseudoneuroptera and 



Neuroptera, is most simple in character, and least different from 

 that of the larval form ; some of these (Panorpa) have an enlarge- 

 ment at the end of the fore-gut; this is the masticatory 

 stomach. The Orthoptera are distinguished by the possession of 

 a stomach of this kind (Fig. 142, A v), which has long rows of 

 chitinous plates on its inner surface. It is also found in the 

 Coleoptera (CarabidaD, Ciciudela), Dytiscidaa, etc.), where it carries 

 setae and ridge-like projections. Many Hymenoptera (Formica, 

 Cynips) also possess it, as do the larvae of the Diptera. 



Another differentiation seen in 

 the fore-gut of many insects (Hemip- 

 tera), which is always short, is an 

 enlargement which may be present 

 all round, or on one side only. When 

 it surrounds the oesophagus it servos 

 as a crop (ingluvies) (i) ; this is the 

 case in many Coleoptera and in the 

 Orthoptera. This dilatation of the 

 fore-gut is found in the Hymenop- 

 tera (Wasps and Bees), but in them 

 it functions as a sucking organ, and 

 leads towards the formation of the 

 Sucking stomach, which is found 

 in other insects. It also forms a 

 vesicular thin -walled appendage, 

 which is attached on the course of, 

 or to the end of the fore-gut; in 

 the Lepidoptera this opens directly 

 (Fig. 141, V), and in the Diptera 

 by means of a stalk of varying 

 length (Fig. 142, B, v s). In the 

 Hymenoptera also an independent and stalked sucking stomach is 

 formed (Crabro). In the Hemiptera it appears to be replaced by 

 an enlargement of the fore-gut, which is frequently multi-sacculate 



(Bugs). 



The mid-gut (" chyle-stomach") is no less varied in character. 

 In many Coleoptera it is provided with short tubes, either along its 

 whole length or in separate segments ; these are known as " glands/' 

 At its commencement we sometimes, and especially in the Orthoptera, 

 find cascal prolongations; as we do also in some families of the 

 Diptera. In the latter it is ordinarily disposed in coils (Fig. 142, B v), 

 in correspondence with its great length. The same occurs also in 

 the long mid-gut of some Coleoptera (e.g. Melolontha), of Bees and 

 Wasps, and of many Hemiptera ; in these forms further divisions 

 are differentiated in it. 



Fig. 142. A Digestive canal of the 

 Field-cricket. B Of a Fly. oe CEso- 

 phagus. i Its crop-like enlargement. 

 v Stomach, c Its appendages, r Hind- 

 gut. vm Malpighiau canals. 



